A pressure sensitive adhesive sheet containing a supporting substrate having coated thereon a pressure sensitive adhesive has been widely used in many fields due to the convenience thereof that the sheet can be easily attached to an adherend by pressing. In recent years, plastic molded articles are being used frequently corresponding to the demands, such as weight saving of products. Associated thereto, there is an increasing use of a pressure sensitive adhesive sheet for attaching to a plastic molded article. Examples of the plastic molded articles include those obtained by molding a resin, such as polycarbonate, polymethyl methacrylate, polystyrene, and ABS.
In the case where a pressure sensitive adhesive sheet (such as a pressure sensitive adhesive label) using a supporting substrate having gas barrier property is attached to the surface of the plastic molded article for such a purpose as decoration, there are cases where a gas is generated from the plastic molded article to form bubbles between the pressure sensitive adhesive sheet and the plastic molded article, which causes blister including lifting. The occurrence of blister impairs the appearance of the label, and the decorative function of the pressure sensitive adhesive sheet is significantly deteriorated.
For solving the problem, for example, PTL 1 describes, as a pressure sensitive adhesive composition, an acrylic pressure sensitive adhesive composition containing a copolymer obtained by radical polymerization of a (meth)acrylate ester, a copolymerizable carboxyl group-containing compound, and a tertiary amine having a vinyl group.
PTL 2 proposes a blister resistant pressure sensitive adhesive sheet using a pressure sensitive adhesive containing a copolymer containing an acrylate ester having an alkyl group having from 4 to 12 carbon atoms and from 0.1 to 10% by weight of a polar monomer, such as acrylic acid and 2-hydroxyethyl acrylate, to which an aziridine cross-linking agent is added.
PTL 3 describes a pressure sensitive adhesive sheet containing, as components forming a pressure sensitive adhesive layer, a pressure sensitive adhesive component and a curing component, which is an acrylic monomer or oligomer, but there are cases where the curing component impairs the cohesive strength of the pressure sensitive adhesive layer, and in the case where the curing component has poor compatibility with the pressure sensitive adhesive component, the pressure sensitive adhesive layer becomes cloudy.
PTL 4 describes a pressure sensitive adhesive composition containing a resin composition obtained by copolymerizing a (meth)acrylate ester having from 1 to 12 carbon atoms and a carboxyl group-containing unsaturated monomer, having the particular molecular weight, and a resin composition obtained by copolymerizing one kind or two or more kinds of a monomer selected from an alkyl methacrylate or cycloalkyl methacrylate having from 1 to 20 carbon atoms, benzyl methacrylate, and styrene, with an amino group-containing unsaturated monomer, having the particular glass transition temperature (Tg) and the particular molecular weight.
PTL 5 describes a blister resistant pressure sensitive adhesive composition containing a copolymer obtained by copolymerizing an alkyl (meth)acrylate having an alkyl group having from 1 to 12 carbon atoms as a major component, a styrene monomer, a carboxyl group-containing unsaturated monomer, and an amino group-containing unsaturated monomer, having the particular molecular weight, with which a cross-linking agent having a glycidyl group is mixed.
PTL 6 describes a resin composition obtained through polymerization in acetone, having a weight average molecular weight of 1,500,000 or more and a ratio (weight average molecular weight)/(number average molecular weight) of 4.0 or less.